Fusion Tipping Point

This news story was published in the World News section of the Super Science issue (issue 28), as one of the most important science stories of the past few months.

A team based at Lawrence Livermore National Laboratories have reached a new milestone in energy output. Recent research, published by Nature, shows that a fusion experiment has produced more energy than the amount put into the fuel – an achievement that has been an ambition of plasma physicists since the 1950’s.

In the $3.5 billion laser-based system, each fusion attempt, or ‘shot’, begins with splitting one weak laser pulse into 192 beams then amplifying each one through special mirrors and crystal optics, before focusing them on the target. The final power of each laser is 4 million joules – the most powerful in the world – and is reached in about 1.5 microseconds.

The target is a poppy seed-sized pellet composed of the hydrogen isotopes tritium and deuterium. The pellet is encased in a 9×5 millimetre gold cylinder called a hohlraum. The beams arrive within picoseconds of one another, entering the top and bottom of the hohlraum. The intense energy of the beams heat the inside, inducing the emission of x-rays from the gold walls and this radiation compresses and heats the plastic shell around the fuel, creating the conditions needed to kick-start the fusion process.

If, or when, the NIF achieves the self-sustaining fuel burn of true ‘ignition’, the announcement will be heralded on front-page headlines around the world; yet this news confirms that the ambitious project is on track. “This is not a multi-decade problem now, if you get to ignition. That’s what’s so exciting”, said Dunne.

That’s what drives me and drives the teams, and a lot of the students who come through can see it happening now,” said Dunne. “The pathway to a power plant is not something their children will do, or grandchildren will do, it’s something that they can do in their research careers.”